1. Field of the Invention
The present invention relates to a polyimide-based solution that can be used to produce an isotropic transparent polyimide-based film with excellent mechanical properties as well as high heat resistance.
2. Description of the Related Art
The fabrication of flexible devices is generally based on high-temperature thin film transistor (TFT) processing. The processing temperatures for the fabrication of flexible devices may vary depending on the kinds of constituent semiconductor layers, insulating films, and barrier layers but TFT processing usually requires a temperature of about 300 to about 500° C. However, the number of polymeric materials capable of withstanding such processing temperatures is extremely limited and polyimides known to have good heat resistance are mainly used for TFT processing.
A flexible device is typically fabricated by applying a polyimide precursor onto a carrier substrate, curing the polyimide precursor to form a film, completing the desired device through subsequent processing steps, and detaching the device from the carrier substrate.
In such fabrication processes, storage stability of the polyimide precursor at room temperature is particularly important. Poor storage stability of the polyimide precursor causes a change in processing viscosity, making the application and curing of the polyimide substrate material unstable. Polyamic acids as polyimide precursors are also known to have poor storage stability due to their structure in which the carboxylic acid groups capable of promoting hydrolysis are adjacent to the amide bonds.
Flexible devices are required to have good heat resistance at high temperatures because their fabrication involves high-temperature processes. Particularly, even organic light emitting diode devices based on low temperature polysilane (LTPSs) processing are often processed at high temperatures close to 500° C. At such temperatures, however, polyimides tend to thermally decompose despite their good heat resistance.
Thus, there is a need to develop a polyimide that can be protected from hydrolysis to achieve good chemical resistance and storage stability and can exhibit good thermal stability at high temperature as well as sufficient mechanical properties, thus being suitable for use in the fabrication of a flexible device.